轨道交通动荷载作用下高温高含冰量冻土路基沉降机理研究

Subsidence of permafrost subgrade, as the main technical obstacle of subgrade maintenance for Qinghai-Tibet Railway (QTR), has caused great attention in the research of the permafrost engineering. Over the decade since the operation of QTR, the ballast thickness, induced by frequently supplementing ballast and elevating ballast, has reached up to 1.7m. Few effective measures have been taken , and the stability of subgrade and the traffic security is being challanged by warm permafrost soil with high ice content. The vibration induced by traffic loads is regarded as one of the main sources leading to the subsidence deformation of subgrade. With the aim at improving the prevention and control theory of permafrost subgrade diseases, the research is intended to focus on the quantitive evaluation of the influence of traffic loads on the high-ice-content warm permafrost subgrade. Nonlinear train-rail-subgrade-ground thermal coupling dynamic model will be constructed based on the unified concept of large scale system, so as to reveal the dynamic and static characteristic of warm permafrost subgrade with high ice content induced by passing trains. Dynamic and static creep models of warm permafrost soil with high ice content will be established by performing laboratory tests, and the feasibility of the built models will be validated by in-situ monitoring and numerical simulation. the subsidence mechanism of permafrost subgrade induced by passing trains will be further illustrated, the forecasting methods of the train-induced subsidence of the warm permafrost subgrade will be provided, and the accumulated deformation of the permafrost subgrade will be forecasted taking into account train-induced settlement, melting subsidence, and compression creep. The research is dedicated to provide scientific insights into the prevention and control of permafrost subgrade diseases, and the dynamic creep model of warm permafrost soil with high ice content subject to traffic loads is original.

多年冻土区路基沉降变形是冻土工程研究中的核心，也是青藏铁路路基维护中的难点。青藏铁路通车近十年不断补碴、抬道使道床厚度甚至达到1.7m以上，部分处理措施效果有限，高温高含冰量冻土造成路基稳定性、行车安全问题日渐凸显。列车行驶振动是路基沉降变形的重要外因之一，本项目以多年冻土路基病害防治理论完善为背景，聚焦定量评价轨道交通动力荷载对高温高含冰量冻土路基影响的科学问题，基于大系统统一分析理念建立列车－轨道－路基－场地热力耦合非线性动力学模型，阐明列车行驶高温高含冰量冻土路基动、静应力特性；采用室内试验建立高温高含冰量冻土动、静蠕变模型，结合现场监测、数值模拟验证模型科学性，揭示列车行驶冻土路基振动沉降机理与发展规律，构建振动沉降预测方法，完成振动沉降与融沉、压缩蠕变共同作用下的累积沉降预测。成果可为冻土地区路基病害治理提供科学依据，其中轨道交通动荷载作用下高温高含冰量冻土动蠕变模型具有原创性。

多年冻土区路基沉降变形是冻土工程研究中的核心，也是青藏铁路路基维护中的难点。青藏铁路通车部分路段不断补碴、抬道使道床厚度甚至达到1.7m以上，部分处理措施效果有限，高温高含冰量冻土造成路基稳定性、行车安全问题日渐凸显。列车行驶振动是路基沉降变形的重要外因之一，本项目聚焦定量评价轨道交通动力荷载对高温高含冰量冻土路基影响。. 首先，基于大系统统一分析理念建立列车－轨道－路基－场地热力耦合非线性动力学三维模型，厘清列车行驶高温高含冰量冻土路基的应力大小、应力路径、频率成分的分布规律与传播特性。发现车辆通过时土单元主应力轴旋转，车辆轴重和路基刚度是影响动应力幅值的主要因素，基床表层动压应力冬季最大，夏季最小，而路基填土深部规律与之相反。. 其次，以青藏沿线砂土和冰为研究对象，进行了应力路径三轴试验和低温静三轴、动三轴试验，建立了考虑轨道交通荷载特征的静力学、动力学蠕变模型，验证了模型的科学性，揭示了砂土相对密实度、体积含冰量、温度和应力路径、振动载荷幅值、频率等因素对青藏砂土力学特性的影响机理。.第三，基于ABAQUS分别建立青藏铁路北麓河高温高含冰量冻土路基水热力大变形融化固结模型和列车行驶振动沉降计算模型，利用监测成果验证科学性，探讨路基沉降影响机理，定量评价青藏铁路DK1136段路基沉降。沉降随路堤高度、富冰冻土层厚度和场地年均地温增大而增大；变形主要来源于多年冻土层融化固结，振动沉降占比20%左右，路堤越低占比越大；填碴抬道养护增加自重，加剧高温高含冰量路基的融化沉降不宜采用，冷却路基是最佳选择。. 最后，完成新型主动通风降温技术理论验证，发明的新型通风管可以埋设在路基任意有利位置，能保障高温高含冰量路段宽幅路基运营30年冷季无融化夹层，夏季人为上限始终在季节活动层内，使多年冻土层始终处于冻结状态，为青藏高速公路等寒区工程建设提供参考。 . 成果可为冻土路基病害治理提供理论依据，对于完善寒区路基设计技术具有现实意义。

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